Slugs

Slugs produce lots of mucus – some covers their whole body and makes it difficult for them to be picked up by a predator, some forms a “slime trail” that aids them when they are moving, and some envelopes their waste. After a slug has eaten and digested food (a wide variety of plants, fungi, earthworms and carrion), a mucus string of scat leaves through its anus, which is hidden under the leathery patch called a mantle, located just behind its head. The odd position of this opening is a result of the slugs’ evolutionary descent from snails. In a snail this opening must be outside the shell, and thus is far forward on its body. (Congratulations to Jean and Michele for their spot-on guesses.)

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Common Gartersnakes mate soon after emerging from hibernation in the spring, in March or April, and four months later the females give birth to live young. The newborn snakes are 5 to 9 inches long at birth and from day one have to fend for themselves. Their diet at this early stage consists of earthworms, insects, slugs, tadpoles, small frogs and fish. If there is an abundant supply of food, the young snakes can grow as much as 1 ½ inches a month during their first year. Earthworms are their preferred diet and gartersnakes are known for their ability to find them, even underground. It turns out that earthworms produce a chemical substance in their skin that is easily detected by (and attractive to) Common Gartersnakes. (Thanks to Eli Holland, who located the worm-eating newborn Common Gartersnake in the photograph.)

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Slugs mate and lay eggs in the spring and fall, and can live 12 to 15 months. Eggs laid in the fall overwinter in this stage, and hatch in the spring. Some members of this generation of slugs may die in the fall, while others hibernate underground or beneath loose bark. The survival rate of the hibernators depends upon the harshness of the winter. Look in and under rotting logs to find slug eggs, and behind the bark of dying trees to find slug hibernacula.

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No-one needs a description of the damage that slugs can do in a garden, but the exact way in which they do the damage is quite unique. They actually do not have mouthparts as such, nor do they possess teeth as we know them. They, like most molluscs, have a radula, or rasping tongue-like organ with which they procure food. A bit of cartilage, the odontophore, forms the core of the radula. The rest of the radula consists of a band, similar to a conveyor-belt, covered with thousands of tiny tooth-like protrusions called denticles. The band moves over the odontophore, rasping away particles of food and moving them back into the slug’s gullet. The pictured slug was making short work of a mushroom.

ADDENDUM TO YESTERDAY’S POST: After several reader comments and self-reflection, I’ve come to the conclusion that yesterday’s post could well be black bear, not raccoon, vomit. While all I found in the cornfield were signs of raccoons, it was a huge field, and I may have just missed bear sign or the bear may well have visited another field prior to getting sick. The amount of vomit was so large that it would have taken a giant raccoon to have left it. Both of these animals feed voraciously in the fall in preparation for winter — black bears can double their weight prior to denning.

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Slugs are hermaphroditic, possessing both male and female organs; most species mate, however, with one slug pursuing the slimy trail of another. If a slug is in mating mode, there is a chemical that is present in its slime that conveys this information to other slugs. When two receptive slugs first encounter each other, there can be extensive interaction prior to mating. The pursuer often mouths the tip of the tail of the slug it’s pursuing (see photograph) to confirm that it’s receptive. The pursued slug may shake its tail vigorously to signal that it’s not interested, in which case they go their separate ways. If the leading slug is receptive, however, mating eventually takes place, with sperm being transferred from each slug to the other through penises that extend half the length of their bodies. During this process, the sexual organs are entwined; occasionally, in some species, the organs get stuck. If this happens, one slug gnaws off the other’s penis in a process called apophallation. The penis is not replaced and the slug lives the rest of its life as a female. (The opening you see on the side of the slug is its respiratory opening, or pneumostome.)

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If you’re looking for a present for someone that will be used year round, year after year, Naturally Curious may just fit the bill. A relative, a friend, your child’s school teacher – it’s the gift that keeps on giving to both young and old!

One reader wrote, “This is a unique book as far as I know. I have several naturalists’ books covering Vermont and the Northeast, and have seen nothing of this breadth, covered to this depth. So much interesting information about birds, amphibians, mammals, insects, plants. This would be useful to those in the mid-Atlantic, New York, and even wider geographic regions. The author gives a month-by-month look at what’s going on in the natural world, and so much of the information would simply be moved forward or back a month in other regions, but would still be relevant because of the wide overlap of species. Very readable. Couldn’t put it down. I consider myself pretty knowledgeable about the natural world, but there was much that was new to me in this book. I would have loved to have this to use as a text when I was teaching. Suitable for a wide range of ages.”

In a recent email to me a parent wrote, “Naturally Curious is our five year old’s unqualified f-a-v-o-r-I-t-e book. He spends hours regularly returning to it to study it’s vivid pictures and have us read to him about all the different creatures. It is a ‘must have’ for any family with children living in New England…or for anyone that simply shares a love of the outdoors.”

I am a firm believer in fostering a love of nature in young children – the younger the better — but I admit that when I wrote Naturally Curious, I was writing it with adults in mind. It delights me no end to know that children don’t even need a grown-up middleman to enjoy it!

Snails and slugs are very similar, except for a slug’s lack of a shell. Both are hermaphroditic, possessing male and female reproductive organs. In some species an individual may behave as a male for a while, then as a female. In a few species, self-fertilization occurs. Some species mate and lay eggs in the spring, some in the fall. Most snails and slugs that hatch in the spring can begin egg laying in the fall. The eggs of both snails and slugs are tiny, white or cream-colored, round and laid in roughly one-inch diameter clusters of 30 or so eggs. Look for these clusters under rotting logs, where they are protected from drying out as well as from freezing. (Remember to place the log back exactly as you found it.)